Mold protective coatings for precision glass molding

Precision Glass Molding (PGM) is a replicative technology to manufacture glass lenses with complex geometries such as aspheres, freeform-optics or lens arrays. During the PGM process, a glass preform is heated until the viscous state and afterwards pressed into the desired shape using two high-precise molds. This process enables the direct and efficient manufacture of high shape accuracy and surface quality optics without any mechanic post-processing step. The efficiency of the PGM process depends primarily on the lifetime of the high-precision molds made of cemented tungsten carbide. During each molding cycle, the molds have to withstand severe thermo-chemical and thermo-mechanical loads. Using protective coatings, the lifetime of the molds can be increased. In this study, the performances of a diamond-like carbon (DLC) and a precious metal alloy coating, namely PtIr, were evaluated in an industrial glass molding machine. The degradation mechanisms of the coatings were analyzed using surface characterization such as scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). At this, phenomena such as glass adhesion and coating disintegration were observed.